William of Sherwood, singular propositions and the hexagon of opposition.
Yurii Khomskii

Abstract:
In Aristotelian logic, the predominant view has always been that there
are only two kinds of quantities: universal and particular. For this
reason, philosophers have struggled with singular propositions (e.g.,
``Socrates is running''). One modern approach to this problem, as
first proposed in 1955 by Tadeusz Czezowski, is to extend the
traditional Square of Opposition to a Hexagon of Opposition.

We note that the medieval author William of Sherwood developed a
similar theory of singular propositions, much earlier than Czezowski,
and that it is not impossible that the Hexagon itself could have been
present in Sherwood's writings.